A conventional traction type elevator includes a cab mounted in a car frame, a counterweight attached to the car frame via a plurality of ropes, and a machine driving a traction sheave that is engaged with the ropes. The ropes used in elevator applications have traditionally been steel wire ropes. Such ropes are inexpensive and durable. A limiting factor in the use of steel wire ropes, however, is their weight. The higher the rise of the building or hoistway, the longer and heavier the rope becomes. The rope gradually begins to dominate the load to be carried by the elevator system until the weight of the rope exceeds the tensile strength of the rope itself. Another disadvantage is the lubrication required for steel wire ropes. The steel wire ropes are treated with an oil lubrication that ultimately becomes deposited on the hoistway equipment, in the machine room, and in the pit of the hoistway.
There has recently been much interest in replacing the traditional steel wire ropes used in elevator applications with ropes formed from high strength, lightweight synthetic materials, such as aromatic polyamid or aramid materials. Lightweight ropes formed from these materials could potentially reduce the size of many elevator components, such as machines and brakes, and could extend the rise of elevators.
The use of such synthetic ropes in traction elevators poses many problems. One of the potential problems is the increased risk of inadvertent damage to the synthetic ropes. Typical aramid materials, such as KEVLAR, have high tensile strength, but the fibers of this type of synthetic rope are more easily abraded and fractured than traditional steel ropes. They are also vulnerable to solvents. A mechanic working in the vicinity of the synthetic ropes may inadvertently come into contact with the ropes with a tool or other abrasive object or with a liquid solvent. This contact may damage the fibers of the rope and reduce the load-carrying capabilities and the expected life of the rope, requiring premature replacement of the ropes.
One solution to this problem is to monitor the wear of the ropes to ensure prompt replacement of any worn ropes, such as suggested in commonly assigned U.S. patent application Ser. No. 08/781,944. This application discloses the use of a plurality of spaced inserts disposed within the rope. The inserts are monitored in various manners to detect elongation of the rope. A mechanism of this type may be used to determine when to discard and replace the ropes.
The above art notwithstanding, scientists and engineers under the direction of Applicant's Assignee are working to develop mechanisms to minimize the risk of damage occurring to elevator ropes.